U.S. patent number 10,096,819 [Application Number 14/429,973] was granted by the patent office on 2018-10-09 for method for forming an electrical connection to a conductive fibre electrode and electrode so formed.
This patent grant is currently assigned to ARCACTIVE LIMITED. The grantee listed for this patent is ArcActive Limited. Invention is credited to John Abrahamson, Shane Christie, Suzanne Furkert, Yoon San Wong.
United States Patent |
10,096,819 |
Abrahamson , et al. |
October 9, 2018 |
Method for forming an electrical connection to a conductive fibre
electrode and electrode so formed
Abstract
A method for forming an electrical connection to a microscale
electrically conductive fiber material electrode element, such as a
carbon fiber electrode element of a Pb-acid battery, comprises
pressure impregnating into the fiber material an electrically
conductive lug material, such as molten Pb metal, to surround
and/or penetrate fibers and form an electrical connection to the
fiber material and provide a lug for external connection of the
electrode element. Other methods of forming a lug for external
connection are also disclosed.
Inventors: |
Abrahamson; John (Christchurch,
NZ), Furkert; Suzanne (Christchurch, NZ),
Christie; Shane (Christchurch, NZ), Wong; Yoon
San (Christchurch, NZ) |
Applicant: |
Name |
City |
State |
Country |
Type |
ArcActive Limited |
Christchurch |
N/A |
NZ |
|
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Assignee: |
ARCACTIVE LIMITED
(Christchurch, NZ)
|
Family
ID: |
50341742 |
Appl.
No.: |
14/429,973 |
Filed: |
September 20, 2013 |
PCT
Filed: |
September 20, 2013 |
PCT No.: |
PCT/NZ2013/000174 |
371(c)(1),(2),(4) Date: |
March 20, 2015 |
PCT
Pub. No.: |
WO2014/046556 |
PCT
Pub. Date: |
March 27, 2014 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20150255783 A1 |
Sep 10, 2015 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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61703442 |
Sep 20, 2012 |
|
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61857729 |
Jul 24, 2013 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H01M
4/747 (20130101); H01M 4/22 (20130101); B22D
19/14 (20130101); B23K 20/02 (20130101); H01M
4/663 (20130101); H01M 10/06 (20130101); C22C
47/12 (20130101); H01M 2/30 (20130101); H01M
4/82 (20130101); H01M 2/266 (20130101); H01M
4/0404 (20130101); C22C 47/066 (20130101); H01M
2/28 (20130101); B23K 20/002 (20130101); H01M
4/0433 (20130101); H01M 10/12 (20130101); Y02T
10/70 (20130101); Y02E 60/10 (20130101); H01M
2220/20 (20130101) |
Current International
Class: |
H01M
4/02 (20060101); C22C 47/06 (20060101); C22C
47/12 (20060101); H01M 2/26 (20060101); H01M
2/28 (20060101); H01M 4/04 (20060101); H01M
4/74 (20060101); H01M 4/82 (20060101); H01M
10/06 (20060101); H01M 10/12 (20060101); B23K
20/00 (20060101); B23K 20/02 (20060101); H01M
2/30 (20060101); B22D 19/14 (20060101); H01M
4/22 (20060101); H01M 4/66 (20060101) |
Field of
Search: |
;429/211 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Harris; Gary
Attorney, Agent or Firm: Dann, Dorfman, Herrell and
Skillman, P.C.
Claims
The invention claimed is:
1. A lead acid battery or cell including at least one electrode
comprising as a current collector a conductive fibre material
having an average interfibre spacing of less than 100 microns,
comprising an electrically conductive lug material pressure
impregnated into a lug zone part of the fibre material surrounding
and/or penetrating the fibres and forming an electrical connection
to the fibre material in said lug zone and providing a lug for
external connection of the electrode element, and comprising an
active material in at least a part of the conductive fibre material
other than in said lug zone, and wherein a surface to volume ratio
of Pb particles in the active material is at least about 3 times
greater than a surface to volume ratio of lug material in the lug
zone.
2. A lead acid battery or cell according to claim 1 wherein the
surface to volume ratio of Pb particles in the active material is
at least about 10 times greater than a surface to volume ratio of
lug material in the lug zone.
3. A lead acid battery or cell according to claim 1 wherein the
surface to volume ratio of Pb particles in the active material is
greater than about 2 m.sup.2/cm.sup.3 and the surface to volume
ratio of lug material in the lug zone is less than about 0.5
m.sup.2/cm.sup.3.
4. A lead acid battery or cell according to claim 1 wherein the
surface to volume ratio of Pb particles in the active material is
greater than about 1 m.sup.2/cm.sup.3 and the surface to volume
ratio of lug material in the lug zone is less than about 0.5
m.sup.2/cm.sup.3.
5. A lead acid battery or cell according to claim 1 wherein the lug
material comprises a metal that is either Pb or a Pb alloy.
6. A hybrid automotive vehicle comprising a battery according to
claim 1.
7. A lead acid battery or cell according to claim 1 wherein active
material contacts the lug where the fibre material enters the lug,
and electrically connects direct to the lug.
8. A lead-acid battery or cell according to claim 1 in which the
electrical resistance of the electrical connection between the lug
material and the conductive fibre material in said lug zone is less
than the resistance of the active material by at least 10% when the
battery or cell is 10% charged.
Description
FIELD OF THE INVENTION
The invention relates to an improved method for forming an
electrical connection to a conductive fibre electrode, such as
battery or cell conductive fibre electrode, and to an electrode so
formed.
BACKGROUND
In a lead-acid battery or cell comprising a carbon fibre electrode
or electrodes, a very low electrical resistance and mechanically
durable connection is required between the carbon fibre electrode
material and a connector or lug (herein generally referred to as
lug) to the external circuit. This can be difficult to achieve
particularly when the carbon fibre electrode material has an
interfibre spacing of less than 100 microns, for reasons that
include that carbon strongly repels metal from its surface and/or
the need to overcome surface tension to enable lug metal to
penetrate between the carbon fibres (whether interfibre or
intrafibre i.e. the latter referring to between filaments of
individual fibres if the carbon fibres are multifilamentary).
Achieving high penetration between fibres to minimise remaining
voidage between the lug material and the fibres of the lug
connection is also important as one way of preventing battery
electrolyte from subsequently entering the lug to fibre connection
and deteriorating the connection.
U.S. Pat. No. 3,926,674 discloses a method for manufacturing
electrical connection elements on battery electrodes of glass fibre
by molten lead injection.
SUMMARY OF INVENTION
In broad terms in one aspect the invention comprises a method for
forming an electrical connection to an electrically conductive
fibre material electrode element having an average interfibre
spacing less than about 100 microns, which comprises pressure
impregnating into a lug zone part of the fibre material, an
electrically conductive lug material to surround and/or penetrate
fibres of the fibre material and form an electrical connection to
the fibre material in said lug zone and provide a lug for external
connection of the electrode element.
In broad terms in another aspect the invention comprises an
electrically conductive fibre material electrode element having an
average interfibre spacing less than about 100 microns, which
comprises an electrically conductive lug material pressure
impregnated into a lug zone part of the fibre material and
surrounding and/or penetrating the fibres and forming an electrical
connection to the fibre material in said lug zone and providing a
lug for external connection of the electrode element.
In broad terms in another aspect the invention comprises an
electrode of a lead acid battery or cell, or a lead-acid battery or
cell comprising at least one electrode, comprising a conductive
fibre material having an average interfibre spacing less than about
100 microns, the electrode comprising an active area and a
conductive element in a lug zone as a connector to the electrode,
in which the electrical resistance of the connection when the
battery or cell is at about 10% charged/90% discharged is less than
the resistance of the active area (when fully charged) by at least
10%.
In broad terms in another aspect the invention comprises an
electrode of a lead acid battery or cell, or a lead-acid battery or
cell comprising at least one electrode, comprising an electrically
conductive fibre material having an average interfibre spacing less
than about 100 microns, the electrode comprising an active area and
a conductive lug element in a lug zone as a connector to the
electrode, in which in the lug zone part of the fibre material, lug
material surrounds and/or penetrates and electrically connects to
the fibres.
In broad terms in another aspect the invention comprises an
electrode of a lead acid battery or cell or a lead-acid battery or
cell comprising at least one electrode, comprising a 3-dimensional
matrix of electrically conductive material extending between an
active area of said electrode and a lug zone as a connector to the
electrode, in which in the lug zone part of the conductive
material, lug material surrounds and/or penetrates and electrically
connects to the conductive material and reduces voidage compared to
voidage in the active area.
In some embodiments the resistance of the lug connection when the
battery is fully discharged is at least 10% lower than the
resistance of the active area.
In broad terms in another aspect the invention comprises an
electrode of a lead acid battery or cell or a lead-acid battery or
cell comprising at least one electrode, comprising a 3-dimensional
matrix of electrically conductive material extending between an
active area of said electrode and a lug zone as a connector to the
electrode, in which in the lug zone part of the conductive
material, lug material surrounds and/or penetrates and electrically
connects to the conductive material and reduces voidage compared to
voidage in the active area.
In some embodiments the collective resistance between the
conductive material and the lug is less than or about the same as
the resistance along the active area.
Typically the conductive fibre material is a non-metallic
conductive material such as a carbon fibre material, such as a
non-woven such as felted carbon fibre material, or a knitted or a
woven carbon fibre material. The material has an average interfibre
spacing less than about 100 microns and in some embodiments less
than about 50 microns, less than about 20 microns, or less than
about 10 microns.
In some embodiments the impregnating material impregnates between
at least about 30%, at least about 40%, at least about 50%, at
least about 70%, at least about 80%, or at least about 95%, or at
least about 98%, or at least about 99% of the fibres.
In some embodiments the interfibre voidage in the fibre material
(being the fraction of the total volume defined by the material
outside dimensions not occupied by the fibres--in the unimpregnated
material) is reduced by at least about 50%, at least about 70%, at
least about 80%, or at least about 95%, or at least about 98%, or
at least about 99%.
In some embodiments the fibres of the conductive fibre material are
multifilament fibres and the impregnating lug material also
penetrates between filaments also reducing intrafibre voidage. In
some embodiments intrafibre voidage is also reduced to about 40%,
to about 30%, to about 25%, to about 20%, or to about 10%, to about
5%, to about 1% of the intrafibre voidage in the unimpregnated
fibre material.
In broad terms in another aspect the invention comprises an
electrode of a lead acid battery or cell or a lead-acid battery or
cell comprising at least one electrode, comprising an electrically
conductive material comprising a matrix of electrically conductive
material extending between an active area of said electrode and a
lug zone as a connector to the electrode, in which in the lug zone
part of the conductive material lug material surrounds and/or
penetrates and electrically connects to the conductive material so
that the lug zone has voidage (being the fractional volume occupied
by the pores between the lead and conductive fibres) of less than
about 30% (over at least a major fraction of the electrode).
In broad terms in a further aspect the invention comprises a lead
acid battery or cell including at least one electrode comprising as
a current collector a conductive fibre material, comprising an
electrically conductive lug material in a lug zone part of the
fibre material surrounding and/or penetrating the fibres and
forming an electrical connection to the fibre material in said lug
zone and providing a lug for external connection of the electrode
element, and comprising an active material in at least a part of
the conductive fibre material other than in said lug zone, and
wherein a surface to volume ratio of Pb particles in the active
material is at least about 3 times greater than a surface to volume
ratio of lug material in the lug zone.
Preferably the surface to volume ratio of Pb particles in the
active material is at least about 5 times greater, or at least
about 10 times greater, at least about 20 times greater, than a
surface to volume ratio of lug material in the lug zone.
Preferably the surface to volume ratio of Pb particles in the
active material is greater than about 2 m.sup.2/cm.sup.3 and the
surface to volume ratio of lug material in the lug zone is less
than about 0.5 m.sup.2/cm.sup.3, or the surface to volume ratio of
Pb particles in the active material is greater than about 1
m.sup.2/cm.sup.3 and the surface to volume ratio of lug material in
the lug zone is less than about 0.5 m.sup.2/cm.sup.3.
In at least some embodiments of a cell or battery employing an
electrode of the invention a low surface to volume ratio of lug
material in the lug zone may be desirable in order to keep the lug
material, such as for example Pb, from being substantially reacted,
for example to PbSO4, during discharge.
In broad terms in a further aspect the invention comprises a lead
acid battery or cell including at least one electrode comprising as
a current collector a conductive fibre material, comprising an
electrically conductive lug material in a lug zone part of the
fibre material surrounding and/or penetrating the fibres and
forming an electrical connection to the fibre material in said lug
zone and providing a lug for external connection of the electrode
element, and comprising an active material in at least a part of
the conductive fibre material other than in said lug zone, and
wherein the active material contacts the lug where the fibre enters
the lug and electrically connects direct to the lug.
Preferably the active material contacts the lug where the fibre
enters the lug and electrically connects direct to the lug through
a thickness of the fibre material, and preferably also along a
major part of or substantially all the length of a boundary between
the lug material and the non-lug material impregnated fibre
material at this boundary.
Pressure Impregnation Lug Forming
In broad terms in another aspect the invention comprises a method
for forming an electrical connection to an electrically conductive
fibre material electrode element having an average interfibre
spacing less than about 250 microns, which comprises pressure
impregnating into a lug zone part of the fibre material, an
electrically conductive lug material to surround and/or penetrate
the fibres and form an electrical connection to the fibre material
in said lug zone.
In broad terms in another aspect the invention comprises an
electrically conductive fibre material electrode element having an
average interfibre spacing less than about 100 microns, which
comprises an electrically conductive lug material pressure
impregnated into a lug zone part of the fibre material and
surrounding and/or penetrating the fibres and forming an electrical
connection to the fibre material in said lug zone.
At least some embodiments comprise heating the lug material and
pressure impregnating it when molten into the fibre material. At
least some embodiments comprise surrounding or enclosing the lug
zone part of the fibre material in a die, pressure impregnating the
molten lug material into the fibre material in the lug zone in the
die, and allowing the lug material to cool and solidify around the
fibres. In at least some embodiments pressure impregnating the
molten lug material into the fibre material includes pressure
impregnating the molten lug material into the die. In other
embodiments the lug material may a thermoplastic or thermoset or
reaction set conductive polymer that is then pressure impregnated
into the fibre material. The die may comprise die parts which are
brought together with the fibre material between, and a closing
pressure or force of the die parts against the fibre material is
less than a pressure impregnating the molten lug material into the
die. In other embodiments pressure impregnating the molten lug
material into the fibre material includes closing a die on the lug
material and fibre material in the die so that the die closing
force pressure impregnates the molten lug material into the fibre
material. In other embodiment on closing the die parts hold the
fibre material in place to assist and/or enable the molten lug
material to pressure impregnate the fibre material.
In at least some embodiments the die comprises a boundary or
periphery part which is more thermally conductive (alternatively
referred to as thermally dissipative) than a non-boundary or
periphery part of the die. In other embodiments the die comprises a
boundary or periphery part which is cooler than a non-boundary or
periphery part of the die. The impregnating material flows towards
the higher thermally conductive or cooler boundary part of the die.
At this boundary part, the impregnating material, including
impregnating material which has flowed/impregnated into the fibres,
cools and solidifies (`freezes`), to reduce or prevent flow of
further molten impregnating material beyond this (frozen) boundary
part. Because the solidified lug boundary part helps reduce the
further flow of molten lug material, less clamping pressure may be
required to contain the molten material in the lug zone of the
fibre material. The boundary or periphery part may be all or part
of the whole boundary or periphery of the lug zone. The die may
comprise two die parts which are brought together with the fibre
material between them and thus the closing pressure or force
applied to the area between the die parts and thus against the
fibre material may be less than an injection pressure of the
impregnating material into the die cavity or the fibre material
because in this embodiment the impregnated material is contained by
a combination of closing pressure of the die parts and such
boundary solidification. The closing pressure on the fibre material
between the die parts may thus be at a level which does not damage
or significantly damage for example structurally damage the fibre
material, by crushing. In some embodiments the die closing force
against the fibre material may result in a pressure against the
fibre material of less than about 240 or about 120 Bar for example
for woven or knitted materials such as carbon woven materials, or
less than about 40 or about 20 Bar when the fibre material is a
non-woven such as for a felt or carbon felt material for example.
In other embodiments die parts may not actually contact the fibre
material, so that there is no pressure (from the die) on the fibre
material during lug impregnation.
In some embodiments a die part on at least one side comprises an
area such as a centre area which has lower thermal conductivity
than the more thermally conductive (or dissipative) or cooler
boundary or periphery part. In some embodiments a die part on at
least one side comprises an area such as a centre area which has a
higher temperature, for example is heated, than the more thermally
conductive or cooler boundary part. In some embodiments such a
centre area of the die part is mounted on a piston or similar,
which is arranged to move to apply force to the molten lug material
after injection and whilst cooling, to increase penetration of the
lug material into the fibre material. The piston arrangement may
also eject the electrode from the die after solidification of the
lug.
In some embodiments a die system is arranged to cause the molten
lug material to enter the fibre material along an edge of the fibre
material. The die (at least when closed) may define a transverse
injection gap through which the molten lug material enters the
fibre material through said edge of the carbon fibre material. The
transverse injection gap may be defined between two opposite die
parts when closed together. In some embodiments the die is open
along a transverse opening opposite or above the transverse
injection gap in the direction of molten lug material movement, and
the fibre material beyond the lug zone extends through said
transverse opening during impregnation. Impregnating the fibre
material may be for a predetermined time and/or predetermined
volume of lug material, and then the injection pressure is
terminated and the lug material in the die allowed to cool and
solidify. In some embodiments a dimension across the die cavity
through a major plane of the carbon fibre material in use is less
than a transverse dimension of the die in the plane of the carbon
fibre material, such as approximately the same as the thickness of
the fibre material to form a thin lug of approximately the same
thickness as the fibre material.
In some embodiments the die is also arranged to form a lug
extension (of solid lug material) beyond an edge of the fibre
material.
In some embodiments remaining voidage if any between the lug and
the fibre material is reduced by impregnating after forming the
lug, a filler which is substantially inert to an electrolyte, or is
separated from bulk electrolyte by a barrier of a material
substantially inert to the electrolyte. In other embodiments the
lug material is substantially inert to an electrolyte eg
titanium.
Conductive Filler Lug Forming
In board terms in another aspect the invention comprises a method
of forming a conductive lug to conductive fibre electrical
connection comprising applying a conductive paste, an encapsulating
material, or an adhesive to a lug zone of the fibre material and
forming a conductive region electrically connected to the fibre
material.
In broad terms in another aspect the invention comprises a
conductive lug to conductive fibre connection formed by applying a
conductive paste, an encapsulating material or an adhesive to a lug
zone of fibre material and causing electrical connection to and/or
into said fibre material with, if required, either heat and/or
pressure, to form a conductive fibre connection in said lug region
with reduced voidage relative to the bulk fibre material.
Electrochemical Lug Forming
In broad terms in another aspect the invention comprises a method
for forming a conductive lug to conductive fibre electrical
connection comprising: applying to the conductive fibre material a
paste which comprises a mixture of lead-based particles, applying
to at least part of a thus pasted part of the conductive fibre
material a metal element, and passing an electric current through
the metal element and through the paste beneath and through the
conductive fibre material beneath at a suitable potential with
respect to the acid electrolyte to form a metal penetration into
the conductive fibre material and connection between the conductive
fibre material and the metal element.
In broad terms in another aspect the invention comprises a
conductive lug to conductive fibre electrical connection formed by
applying a paste which comprises a mixture of lead-based particles
to the conductive fibre material, applying to at least a part of a
thus pasted part of the conductive fibre material the metal
element, and passing an electric current through the metal element
and through the paste beneath it and gradually to at least said
part of the conductive fibre material at a suitable potential with
respect to the acid electrolyte to form a metal penetration into
the conductive fibre material and connection between the conductive
fibre material and the metal element.
In some embodiments the paste comprises Pb-sulphate particles, PbO
particles, Pb particles, or a mixture of Pb-sulphate particles,
and/or PbO particles, and/or Pb particles, or a mixture of zinc and
zinc oxide particles, or Cd or Cd(OH)2 particles. Circuit
connections for the electro chemical paste conversion, may be made
to the metal element and a part of the fibre material for example
one edge of the fibre material, or to the metal element and two or
more parts of the fibre material for example two edges such as two
opposite edges of the fibre material. During the step of passing an
electric current through the metal element or connector and at
least said part of the conductive fibre material to connect the
conductive fibre material and the connector, the Pb-based particles
in the paste convert to lead first just beneath the connector and
gradually intimately between the fibres beneath the connector and
thus to connect or electrically connect the fibres and the metal
element or connector.
General
In all embodiments above the conductive fibre material may be a
non-woven material such as a felt material, a woven material
(comprising intersecting warp and weft fibres), or a knitted
material. The material may be a carbon fibre material, such as a
non-woven, knitted, or woven carbon fibre fabric, or alternatively
a glass fibre or silicon based fibrous material. The fibres, for
example, carbon fibres are typically multifilamentary but may be
monofilament. In some embodiments the fibre material has an average
interfibre spacing of less than about 250 microns, or less than
about 100 microns, less than about 50 microns, less than about 20
microns, or less than about 10 microns. The fibre diameter may be
in the range from about 1 micron to about 30 microns, from about 4
microns to about 20 micron, from about 5 microns to about 15
microns. The voidage in the (unimpregnated) material may be at
least about 80% or at least about 95% for example, to about 2% for
example.
In some embodiments the impregnating lug material is a metal. In
one embodiment the metal is Pb or a Pb alloy (herein both referred
to inclusively as Pb). In another embodiment the metal is a Zn or a
Zn alloy (herein both referred to inclusively as Zn). In another
embodiment the metal is Cd or a Cd alloy (herein both referred to
inclusively as Cd). Alternatively the impregnating lug material may
be a conductive polymer for example.
In some embodiments the conductive fibre material may be carbon
fibre material which has been treated by electric arc discharge.
The carbon fibre material may be electric arc treated by moving the
carbon fibre material within a reaction chamber either through an
electric arc in a gap between electrodes including multiple
adjacent electrodes on one side of the material, or past multiple
adjacent electrodes so that an electric arc exists between each of
the electrodes and the material. In other embodiments the carbon
fibre material for use as the electrode current collector material
may be thermally treated at an elevated temperature for example in
the range 1200 to 2800.degree. C. Such treatment may increase
electrical conductivity of the material.
In some embodiments the conductive fibre material has been woven,
or knitted, from multifilament carbon fibre which has been: split
from a higher filament count bundle of carbon fibres (`tow`), into
smaller tows, or stretch broken to break individual continuous
filaments into shorter filaments and separate lengthwise the ends
of filaments at each break, reducing the filament count of the
carbon fibre tow, or split from a higher filament count bundle of
carbon fibres (`tow`), into smaller tows, and then stretch broken
to break individual continuous filaments into shorter filaments and
separate lengthwise the ends of filaments eat each break, further
reducing the filament count of the carbon fibre tows.
In a cell or battery, the positive electrode or electrodes, the
negative electrode or electrodes, or both, may be formed of one or
more layers of the conductive fibre material with a lug, in
accordance with the invention. The invention has been described
herein sometimes with reference to electrodes of Pb-acid batteries
but may also have application to other battery types such as Li-ion
batteries, and in other applications such as in electrodes in solar
cells, or in capacitors or supercapacitors, for example.
In some embodiments the invention comprises a hybrid automotive
vehicle comprising a lead acid battery of the present invention
and/or made in accordance with the methods taught herein. In other
embodiments the hybrid automotive vehicle has stop-start and/or
regenerative braking functionality. In other embodiments the
battery can carry accessory loads when the vehicle engine is
off.
In this specification `lug` means any electrically conductive
element or connector which enables external connection of the
conductive fibre electrode, regardless of physical or mechanical
form.
In this specification `lug region` and `lug zone` are used
interchangeably and have the same meaning.
In this specification "matrix" in relation to the lug refers to lug
material encapsulating the conductive fibre material in the lug
zone in a 3-dimensional structure that has length, width and
depth.
In this specification "hybrid vehicle" refers to a vehicle that
incorporates any one of idle elimination (stop-start
functionality), regenerative braking, and any combination of an
internal combustion engine with an electric motor where one or the
other or both can provide a drive functionality, a hybrid vehicle
may also include a vehicle that may only be a partial hybrid
vehicle.
The term "comprising" as used in this specification means
"consisting at least in part of". When interpreting each statement
in this specification that includes the term "comprising", features
other than that or those prefaced by the term may also be present.
Related terms such as "comprise" and "comprises" are to be
interpreted in the same manner.
BRIEF DESCRIPTION OF THE FIGURES
Embodiments of the invention are further described with reference
to the accompanying figures by way of example wherein:
FIG. 1 shows part of a carbon fibre material electrode with a Pb
lug formed by a first pressure impregnating embodiment of the
invention,
FIG. 2 is schematic cross-section of an electrode comprising
multiple layers of carbon fibre material and a lug,
FIGS. 3-1 to 3-7 schematically show a series of steps for forming a
lug on an electrode of fibre material according to the first
pressure impregnating embodiment of the invention,
FIGS. 4A and 4B are schematic views of the inside faces of two
opposite die parts of one embodiment of a die,
FIGS. 5A and 5B are schematic cross-section views along line I-I of
FIG. 4A and line II-II of FIG. 4B respectively of the back and
front plates of another embodiment of a die,
FIGS. 6A and 6B, 7A and 7B, and 8A and 8B are SEM images of lugs
formed by the first pressure impregnating embodiment of the
invention and as referred to further in the subsequent description
of experimental work,
FIG. 9 shows a carbon fibre material electrode with another form of
Pb lug formed by a second pressure impregnating embodiment of the
invention,
FIG. 10 is a view of the carbon fibre electrode of FIG. 9 in the
direction of arrow F thereof,
FIG. 11 is an expanded schematic cross-section view of a die to
form a lug of the form of FIGS. 9 and 10,
FIGS. 12A and 12B are schematic views of the inside faces of two
opposite die parts of the die of FIG. 11,
FIG. 13 is a schematic cross-section view along line of FIG. 11 but
of one die part only (left hand part in FIG. 14),
FIG. 14 is a schematic cross-section view along line IV-IV of FIG.
11 (both die parts),
FIGS. 15-1 to 15-6 schematically show a series of steps for forming
a lug on an electrode of fibre material according to the second
pressure impregnating embodiment of the invention,
FIG. 16 is a schematic cross-section of a die to form a lug on an
electrode of fibre material, according to a third pressure
impregnating embodiment of the invention,
FIG. 17 schematically illustrates steps of an embodiment for
electrochemically forming a lug on a fibre material electrode,
FIG. 18 is a perspective view of an electrode produced by the
method of FIG. 17,
FIGS. 19 and 20 are SEM images of lugs formed by the second
pressure impregnating embodiment of the invention and as referred
to further in the subsequent description of experimental work,
and
FIG. 21 shows results of CCA performance testing referred to in the
subsequent description of experimental work.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS
Pressure Impregnated Lugs
FIG. 1 shows a section of a conductive fibre electrode such as of
carbon fibre, for a Pb-acid cell or battery for example, with one
form of lug such as a Pb lug, formed on the fibre material by a
first pressure impregnating embodiment of the invention. The fibre
material is indicated at 1 and the lug at 2. The lug may have a
similar thickness (dimension through the plane of the material) to
the fibre material thickness or a greater thickness. FIG. 2 is a
schematic cross-section of a similar electrode comprising multiple
layers 1 of fibre material, and a lug 2. In both embodiments the
lug has a lug extension 3 beyond the edge of the fibre material,
comprising lug material only ie solid lug material such as Pb.
FIGS. 9 and 10 show a conductive fibre electrode such as of carbon
fibre, for a Pb-acid cell or battery for example, with another form
of lug such as a Pb lug, formed on the fibre material by a second
pressure impregnating embodiment of the invention. The fibre
material is again indicated at 1 and the lug at 2. The lug 2
comprises a portion 4 (the lug zone of the electrode) in which the
fibre material is impregnated by the lug material, and a lug
extension 3 beyond the edge of the fibre material, comprising lug
material only. In the embodiment shown the lug has a similar
thickness (dimension through the plane of the material) to the
fibre material thickness and the lug may be not thicker than the
carbon fibre material.
The lug is typically formed of metal such as Pb or a Pb alloy, Zn
or a Zn alloy, or Cd or a Cd alloy, but may alternatively be formed
of other lug material such as a conductive polymer for example.
In the embodiment shown the lug extends along a single edge of the
electrode, which is a single upper edge, but alternatively the lug
may extend along two or more edges of the electrode, the lug may be
curved or arcuate in shape, and/or may be formed to extend across a
centre area of an electrode.
In some embodiments substantially all or at least a majority of the
fibres of the electrode material extend continuously across the
electrode to or through the lug.
The fibre material may be a non-woven such as felt, knitted, or
woven fibre fabric, in particular a non-woven such as felt,
knitted, or woven carbon fibre fabric. Alternatively the material
may be a glass fibre or silicon based fibrous material, which may
be coated with a conductive material typically metal, such as a Pb
film or coating. The fibres, for example carbon fibres, are
typically multifilamentary but may be monofilament. In at least
some embodiments the fibre material has an average interfibre
spacing of less than about 250 microns, less than about 100
microns, less than about 50 microns, less than about 20 microns, or
less than about 10 microns. In at least some embodiments the fibre
diameter is in the range from about 1 micron to about 30 microns,
from about 4 microns to about 20 micron, or from about 5 microns to
about 15 microns. The voidage in the (unimpregnated) material may
be in the range of from about 50% to at least about 1%, from about
40% to about 1%, or from about 30% to about 1%.
In some embodiments the impregnating material impregnates between
at least about 50%, at least about 70%, at least about 80%, or at
least about 95% of the fibres.
In some embodiments the interfibre voidage in the fibre material
(being the fraction of the total volume defined by the material
outside dimensions not occupied by the fibres--in the unimpregnated
material) is reduced by impregnation of the lug material between
into the interfibre voidage between the fibres, at least about 50%,
at least about 70%, at least about 80%, at least about 95%, at
least about 98%, or at least about 99%.
In some embodiments the fibres of the fibre material are
multifilament fibres and the impregnating lug material also
penetrates between filaments also reducing intrafibre voidage. In
some embodiments intrafibre voidage is also reduced to about 40%,
to about 30%, to about 25%, to about 20%, to about 10%, to about
5%, or to about 1% of the intrafibre voidage in the unimpregnated
fibre material.
A matrix of the lug material encapsulates the microscale carbon
fibre electrode material in the lug zone. A very low electrical
resistance connection is formed between the microscale carbon fibre
electrode material and lug. Also voidage between the lug material
and the fibres is minimised, preventing or minimising battery
electrolyte from subsequently entering the lug to fibre connection
and deteriorating the connection, so the connection is more
durable.
Optionally any remaining (open cell/porous) voidage between the lug
material and the fibres and/or filaments may be reduced by filling
with a material which is substantially inert to the electrolyte,
such as for example a non-conductive polymer such as an epoxy.
Optionally the impregnating material (not inert to an electrolyte)
is protected from the bulk of the electrolyte by an inert material
barrier.
Optionally also the impregnating lug material may be a material
which is electrically conductive but substantially inert to a
battery electrolyte such as a Pb acid battery electrolyte such as
titanium.
The conductive or carbon fibre material may have a thickness
(transverse to a length and width or in plane dimensions of the
electrode) many times such as about 10, 20, 50, or 100 times less
than the or any in plane dimension of the electrode. The thickness
may be less than about 5 or less than about 3 mm or less than about
2 mm or about or less than about 1 mm or about 0.2 mm for example.
Each of the in plane length and width dimensions of the electrode
may be greater than about 50 or about 100 mm for example. Such
electrodes have a planar form with low thickness. In preferred
forms the electrode is substantially planar and has a dimension
from a metal lug for external connection along at least one edge of
the electrode less than about 100 mm or less than about 70 mm, or
less than about 50 mm, or about 30 mm or less for example (with or
without a macro-scale current collector). Alternatively such a
planar form may be formed into a cylindrical electrode for
example.
Pressure Impregnation Lug Forming
FIGS. 3-1 to 3-7 schematically show a series of steps for pressure
impregnating a microscale fibre material to form a lug of the form
of FIGS. 1 and 2, FIG. 4A is a schematic view of the inside face of
the die part shown on the left in FIGS. 3-1 to 3-7, and FIG. 4B is
a schematic view of the inside face of the die part shown on the
right in FIGS. 3-1 to 3-7. The lug is formed by pressure
impregnating lug metal into a lug zone part of the fibre material
to penetrate into and form an electrical connection to the fibre
material in the lug zone. Referring to FIGS. 3-1 and 4A and 4B, in
the embodiment shown the die comprises two die parts 10 and 11 with
internal cavities 12 and 13. The die parts 10 and 11 close together
and open reciprocally in operation in the direction of arrow A.
(see FIG. 3A). The die parts are brought together with the fibre
material, indicated at 1 in FIG. 3, between and extending through
the die cavity as shown. FIG. 3-1 shows the die open ie the two die
parts separated, and FIG. 3-2 shows the two die parts closed
against the fibre material but before lug metal injection. One (or
both) of the die parts may comprise a peripheral protrusion or wall
14 (boundary or periphery part of the die) around the cavity which
when the die parts close together contacts the carbon fibre around
a periphery or boundary part of the lug zone of the fibre material.
However the closing pressure or force between the die parts and
thus against the fibre may be at a level which does not damage or
significantly damage for example structurally damage the fibre
material, by crushing. The closing pressure may be less than the
injection pressure of the molten metal into the die cavity. In some
embodiments the pressure against the fibre material may be (only)
about 5 Bar, for example for woven carbon fibre materials, or up to
only 5 Bar non-woven carbon fibre material such as felt material
for example. In one embodiment the die parts may not touch the
fibre material but may when the die is closed be closely spaced for
example less than 0.5 mm or less than 0.25 mm from the surface of
the fibre material. Such a gap may allow the lug material to flow
around the outside surfaces of the fibre material, but should be
sufficiently small that this lug material will quickly cool and
solidify (freeze) so that further injected lug material is then
pressure impregnated into the fibre material. Alternatively the die
parts may contact the fibre material when closed but with no
pressure/compression of the fibre material.
Referring to FIG. 3-3 lug metal 2a is heated and impregnated into
the die cavity through one or more ports and preferably a port such
as indicated at 15 which delivers molten lug metal into a central
area of the cavity as shown. The impregnating pressure causes the
molten metal to penetrate between the microscale fibres in the lug
zone, and is maintained at a level so that molten metal will pass
from the injection side 11 of the die cavity, and between the
fibres in the lug zone, to fill the cavity between the two sides of
the die cavity, so that a lug with metal on both sides of the fibre
material is formed and with metal penetrating between the fibres ie
at least partially filling the interfibre voidage, and preferably
also penetrating into the fibres if the fibres are multifilamentary
fibres ie filling at least partially the intrafibre voidage.
Alternatively metal may be impregnated from both sides or from an
edge of the die cavity.
When the penetrating metal reaches the boundary part 14 of the die
cavity or lug zone of the fibre material, the penetrating molten
metal at or adjacent and around the boundary part 14 cools and
solidifies ie freezes. This cooled and solidified boundary metal of
the forming lug prevents further penetration of molten lug metal
into the fibre material beyond boundary part 14, and therefore the
clamping pressure between the two die parts may be less than the
injection pressure of the impregnating material or metal. The metal
in the die cavity ie the formed lug 2, is then allowed to cool and
solidify as shown in FIGS. 3-5 and 3-6 to form a complete (solid)
lug as shown in FIGS. 3-6, and the die is then opened as shown in
FIG. 3-7 to release or eject the fibre material with a solidified
metal lug thereon.
In some embodiments cooling and solidification first of the lug
periphery is achieved by the boundary or periphery part of the die,
such as the protrusion or wall 14, being more thermally conductive
(or thermally dissipative) than a central area of the die cavity.
In other embodiments the boundary part is held at or cooled to a
lower temperature than a central area of the die cavity by ducts in
the die parts through which a cooling fluid is circulated for
example.
In the embodiment shown in FIGS. 3-1 to 3-7, the die part 10 has a
cavity 12 opposite the injection port 15 which is held at or cooled
to a lower temperature lower than the melting temperature of the
lug material injected. The die part 10 also is provided with a
thermal insulating insert 17. The temperature of the other die part
11 with injecting port 15 is held closer to the melting point of
the lug metal to prevent the injected molten metal solidifying
prematurely. Referring to FIG. 3-5, when molten metal first flows
into and begins filling the die cavity, in the centre of the die
cavity it contacts the insulating thermal insert 17 which prevents
the molten metal from cooling and solidifying too quickly in the
centre of the die cavity. Thus the molten metal in the centre of
the die cavity continues to flow under the injection pressure,
outwardly toward the periphery of the die cavity, to fill the
entire die cavity and to penetrate the carbon fibre in the die
cavity (and freezes first at the boundary as described above).
Alternatively instead of providing the insulating 17 the central
area of the die cavity may be heated during the metal injection
relative to the boundary 14 of the die cavity.
FIG. 5A is a schematic side cross-section view of die back plate
part 10 along line I-I of FIG. 4A showing thermal insulating
material 17 in the centre of the die cavity mounted on a piston 18.
This piston can move in the direction of arrow A to compress the
molten impregnated material into the fibre material prior to
freezing, to further reduce voidage, and can also operate to eject
the formed lug once the die plates have opened.
FIG. 5B is a schematic side cross-section view of die front plate
part 11 along line II-II of FIG. 4B. In this embodiment thermal
insulating material 17a is provided in the centre of the injection
part side of the die and around injection port 15.
FIGS. 11 to 15 schematically show pressure impregnating by a second
embodiment to form a lug of the form of FIGS. 9 and 10. FIGS. 11 to
14 are schematic cross-section views of a die system, and FIGS.
15-1 to 15-6 schematically show a series of steps for forming a
lug.
Again the lug is formed by pressure impregnating into a lug zone
part of fibre material to form a conductive penetration into and
connection to the fibre material in the lug zone. The die comprises
two die parts 20 and 21 which close together and open reciprocally
in operation in the direction of arrow B. The die comprises
internal cavity 22. The die (when closed) comprises a transverse
flow conduit 23 below the cavity 22 (below in the direction of
molten material movement C--as will be further described). The
transverse flow conduit 23 is made up of transverse cavities 23a
and 23b in the opposite die parts. Both die cavity 22 and flow
conduit 23 below extend transversely across the die (see FIGS. 12
and 14) and they are separated by a transverse projection 25 in one
die part 21 part way across the die cavity 22. When the die parts
20 and 21 are brought together the top of the die cavity is open at
24.
In operation the die parts 20 and 21 are brought together with an
edge of fibre material 1 on which a lug is to be formed in the die
cavity as shown in FIG. 11 (though FIG. 11 shows the die open). The
balance of the fibre material 1 extends from the open transverse
slot 24. Lug metal 2a is heated and impregnated into the die cavity
through injection port 26 which delivers molten metal into flow
conduit 23 extending transversely across the die, which it fills.
Molten metal then exits flow conduit 23 transversely across the die
moving in the direction of arrow C in FIG. 11, and flows through a
transverse injection gap past transverse protrusion 25 also
extending across the die, and impregnating the fibre material 1
along and through its edge. The molten metal penetrates the fibre
material in the lug zone. Cooling ducts 28 are provided in the die
parts 20 and 21 through which cooling fluid is circulated to cool
the die above the lug zone of the fibre material in use. The front
of molten metal moving up the die cavity 22 and into the fibre
material 1 cools and solidifies ie freezes, and the resulting
transverse line of solid metal across the die prevents further
penetration of the metal into the fibre material and defines the
limit of the metal lug. After a predetermined time period the
injection pressure is terminated and the Metal in the die cavities
23 and 22 allowed to cool and solidify, and the die is then opened
to release or eject the carbon fibre material with a metal lug
thereon.
FIG. 15-1 shows the die open ie the two die parts 20 and 21
separated, and FIG. 15-2 shows the two die parts closed against the
fibre material 1 but before metal injection. FIG. 15-3 shows hot
metal 2a entering the die cavity through port 26 and filling
conduit 23 across the width of the die. FIG. 15-4 shows molten
metal entering die cavity 27 and penetrating the carbon fibre. FIG.
15-5 shows the metal cooling to solidify the lug on the carbon
fibre 1, and FIG. 15-6 shows the die opening to release the carbon
fibre material with a metal lug thereon.
The dimension across the die cavity 27 between the two die parts 20
and 21 may be approximately the same as the thickness of the fibre
material to form a thin lug of approximately the same thickness as
the fibre material, as described previously or greater to form a
thicker lug. Again, the closing pressure or force between the die
parts and thus against the fibre may be at a level which does not
damage or significantly damage for example structurally damage the
fibre material, by crushing. In some embodiments the pressure
against the fibre material may be (only) about 5 Bar, for example
for woven carbon fibre materials, or up to only 5 Bar non-woven
carbon fibre material such as felt material for example. In one
embodiment the die parts may not touch the fibre material but may
when the die is closed be closely spaced for example less than 0.5
mm or less than 0.25 mm from the surface of the fibre material.
Such a gap may allow the lug material to flow around the outside
surfaces of the fibre material, but should be sufficiently small
that this lug material will quickly cool and solidify (freeze) so
that further injected lug material is then pressure impregnated
into the fibre material. Alternatively the die parts may contact
the fibre material when closed but with no pressure/compression of
the fibre material.
FIG. 16 is a schematic cross-section of a die to form a lug on an
electrode of fibre material, according to a third pressure
impregnating embodiment of the invention. In this embodiment the
pressure which impregnates the molten lug material into the fibre
material is generated by closing a die on the lug material and
fibre material in the die. Referring to FIG. 16, die parts 80 and
81 move reciprocally as indicated by arrows D on a machine bed 82
(the figure shows the die open). Duct(s) 89 which carry cooling
fluid are provided along a distal part of each die part 80 and 81.
Alternatively the distal parts of the die parts 80 and 81 may be
formed of a material which dissipates heat more quickly for
example.
In operation the edge of fibre material 1 on which a lug is to be
formed is positioned in the die cavity between the die parts 80 and
81 as shown. The balance of the fibre material extends from the
open transverse slot 85. Lug metal is also pre-positioned in the
die cavity. For example in the figure two strips 88 of lug material
are shown interleaved between three fibre material layers 1. The
die parts 80 and 81 are heated and are and brought together to
close the die, heating the lug metal under pressure, which melts
and penetrates the fibre material 1 in the lug zone. Molten lug
metal moving through the fibre material in the direction of arrow E
cools and solidifies ie freezes adjacent the duct(s) 89, and the
resulting transverse line of solid metal in the fibre material
across the slot die opening prevents further penetration of the
metal into the carbon fibre material and defines the limit of the
metal lug. After a predetermined time period the injection pressure
is terminated and the metal in the die cavity allowed to cool and
solidify, and the die is then opened to release or eject the carbon
fibre material with a metal lug thereon.
In all embodiments above, to aid impregnation of the fibre material
by the lug metal under pressure, vibration or energy may be applied
to the molten lug metal via one or more die parts during
impregnation, for example at an ultrasound frequency such as a
frequency in the range about 15 to about 25 kHz.
Battery or Cell Construction
A lug formed on fibre material electrode as described above may
also comprise on one or both sides of the fibre material a metal
wire or tape electrically conductively attached to the electrode
material and to the lug, to provide an additional macro-scale
current collecting pathway from the carbon fibre to the metal lug,
in addition to the micro-scale pathways through the carbon fibre
material itself of the lug. The metal wire or tape may be attached
to the fibre material for example by stitching or sewing with a
thread that will not dissolve in battery electrolyte, or other
inert Pb acid battery binding material that will hold the current
collector in place, such as a resin, cement or potting mix. The
metal wire or tape may be pressed into the fibre material during
manufacture. Alternatively the wire or tape or similar may be
soldered to or printed on the fibre material. The metal wire or
tape(s) may be arranged in a sinuous shape on one or both sides of
the fibre material, extending continuously between the lug at one
edge of the electrode, at which edge the wire or tape is
conductively connected to the lug by being embedded in the lug, and
at or towards another spaced edge of the electrode. Alternatively
the wire or tape may extend between metal lugs along opposite edges
of the electrode or a frame around the electrode. Alternatively
again separate lengths of the wire or tape may extend from the lug
at one edge to or towards another edge of the electrode, or
alternatively again the wire or tape macro-conductor as described
may comprise a metal mesh attached on one or both sides of the
fibre material. The ends of the wire or tape or mesh may terminate
and be embedded in the lug. It is important that when the current
collector is on the outer surface of the electrode that acts as the
negative electrode the current collector is protected from anodic
oxidation from the positive electrode. Preferably the wire or tape
runs up and down the length of the electrode with equal spacing
across the width of the electrode without any cross over points, to
prevent local hotspots occurring or heat build up in particular
areas, and an even current collection across the electrode.
Preferably the volume of the wire or tape or mesh or similar
macro-scale current collecting system is less than about 15% of the
volume of the electrode (excluding the lug or surrounding metal
frame or similar).
Typically during battery or cell construction the microscale
current collector material is impregnated under pressure with a
paste, which in a preferred form comprises a mixture of Pb and PbO
particles of Pb and PbO and dilute sulfuric acid. Alternatively the
paste may comprise lead sulphate (PbSO.sub.4) particles and dilute
sulphuric acid. In some embodiments the paste at impregnation into
the electrode comprises dilute sulphuric acid comprising between
greater than 0% and about 5%, or between 0.25% and about 3%, or
between 0% and about 2%, or between 0.5 and 2.5% by weight of the
paste of sulphuric acid. The Pb-based particles may comprise milled
or chemically formed particles which may have a mean size of 10
microns or less, small enough to fit easily into spaces between the
fibres. The paste or active material may fill the carbon fibre
electrode up to the lug so that the active material contacts or
abuts the lug where the fibre enters the lug and electrically
connects direct to the lug, not only at the surface of the fibre
material on either side but also through the thickness of the fibre
material, and along a major part of or substantially all the length
of the boundary between the lug material and the non-lug material
impregnated fibre material at this boundary, or may stop short of
the lug so that there is a small gap between the paste and the lug
such as a gap of up to about 5 mm for example. In a preferred
embodiment the lug is formed so as to have protrusions of the lug
such as Pb protrusions, into the active material impregnated into
the carbon fibre material, as described above.
As stated preferably the surface to volume ratio of Pb particles in
the active material is at least about 3 times greater, or
preferably about 5 times greater, or preferably about 10 times
greater, or preferably about 20 times greater, than a surface to
volume ratio of lug material in the lug zone. Preferably the
surface to volume ratio of Pb particles in the active material is
greater than about 2 m.sup.2/cm.sup.3 or greater than about 1
m.sup.2/cm.sup.3 and the surface to volume ratio of lug material in
the lug zone is less than about 0.05 m.sup.2/cm.sup.3. The surface
associated with molten lug material that has been injected into
fibre layers, cooling as it enters, is likely to be similar to the
surface area of the fibres that it will cool around, or less. For
example, a carbon felt may have an area of the cylindrical surfaces
of the fibres equal to around 20 m.sup.2 per mm thickness for 1
m.sup.2 of superficial area, which is equivalent to 0.02 m.sup.2
per cm.sup.3 of felt total volume. Thus flowing molten lead around
this fibre network will form (by freezing onto the cold fibres
first) a lead structure with branches larger in diameter than the
diameter of the fibres ie. the diameter of the branches of this
lead-loaded felt may increase from 10 microns to around 15 to 20
microns with surface area perhaps 0.01 m.sup.2 per cm.sup.3 (for
higher volume fraction impregnation these branches will merge and
the surface will decrease even further). These surface areas can be
compared with those for the normal active material within a
negative electrode in a lead-acid cell. Lead-containing active mass
is divided into a lead skeleton that carries current (which is not
susceptible to electrochemical change during charge and discharge
cycles) and a much finer mass that is susceptible to change and in
fact produces the working electrical currents of the battery. The
much finer "energetic active material" may have around 0.3 micron
diameter branches. The skeleton may be very similar to the branches
formed by partial impregnation above, with negligible
electrochemical attack. However the surface area of the fine
electrochemically active material may have (20)/0.3)=70 times the
surface area per unit volume of lead, and so suffers almost all the
chemical attack. The division between fine material and coarse
skeleton material is around 50/50% in most negative electrodes.
Electrochemical Lug Forming
Referring to FIG. 17 in an embodiment of an electrochemical lug
forming method of the invention as applied to a Pb-acid battery or
cell electrode, a carbon or conductive fibre material element such
as an electrode element has applied thereto a paste which comprises
lead-based particles--in FIG. 17 the thus pasted element 61 is
indicated at step 17-1. The paste may be impregnated into the fibre
material under pressure and/or with vibration such as ultrasonic
vibration to fully impregnate the paste between fibres. Optimally a
curing process may then be undertaken, where for example the
humidity and/or temperature is controlled.
The paste may comprise Pb-sulphate particles, PbO particles, Pb
particles, or a mixture of Pb-sulphate particles, PbO particles,
and/or Pb particles. In preferred embodiments this paste is
substantially the sole source of lead in the active material paste.
The particles may comprise milled or chemically formed particles
and at least a major fraction of and preferably at least 80% of the
particles may have an average size or diameter of 10 microns or
less. The paste may optionally also contain other additives such as
carbon black, barium sulphate and sulphonate.
The fibre surfaces of the material may be surface treated to
enhance attachment of the Pb-based particles by processing to
attach oxide particles or oxygen bearing chemical groups to the
fibres. Anodic oxidation of electric arc-treated carbon fibre
fabric also may convert it to a hydrophilic material. This may
assist an even distribution of the active particles through the
material and initial attraction of the Pb (covered with oxide
groups) to the carbon, by dipole-dipole attractions.
As indicated at FIG. 17 step 17-2, a metal or conductive connector
or connectors 62 comprising for example metal strips or in any
other suitable form are mechanically attached to the pasted carbon
fibre element 1 for example along at least one edge or
alternatively extending across the carbon fibre element. Thus an
area 63 of the pasted material is captured by the connectors 62.
The strips may for example be crimped to the material edge or
otherwise mechanically fixed to the material, with for example,
compression, heating such as by induction or resistive heating, as
indicated at step 17-3. Alternatively or additionally metal
strip(s) may be provided between each of two or more layers of
carbon fibre material forming the carbon fibre element 1.
Alternatively again metal fibres may be incorporated in the edge of
the carbon fibre element 1 for example by weaving into the carbon
fibre material at or near the edge.
As indicated at step 17-4 the pasted carbon fibre element 1 with
connector(s) 62 is dipped into dilute sulphuric acid in a cell 64,
to cover the top of the connector, and connected as the negative
electrode opposite another electrode polarised positively. An
electric current is passed through the connector(s) 62 and the
material 1 to electrically connect the fibres and the connector(s)
by electrochemically converting the paste in area 63 into a Pb
network. This forms Pb between the carbon fibres and overcomes the
surface tension problems between Pb and carbon fibres in methods
currently available. Alternatively in some embodiments the paste
comprises dilute sulphuric acid, or is contacted with dilute
sulphuric acid for example by spraying dilute sulphuric acid onto
the carbon fibre element material instead of dipping. The electric
current passing through the connector(s) and the carbon fibre
element material and the dilute sulphuric acid-wetted paste
between, causes the Pb-based particles in the paste to convert to
lead first just beneath the connector and gradually intimately
between the electrode material fibres in area 63, to connect or
electrically connect the fibres there with the connector. Typically
this step may be carried out at the start of initial electrode
formation (first charge and discharge cycle during which active
particle linkages form) before or after cell or battery
construction. Thus the same conduction-forming process occurring in
area 63 propagates to the remainder of the electrode. It may be
advantageous that during formation the charging current is pulsed
periodically.
In the embodiments described above the connector 62 is a metal
strip such as a Pb strip mechanically attached to the carbon fibre
element. In an alternative embodiment each of the connectors 62 is
replaced by a mechanical fastening device for example a clamp
having leady surfaces of the same desired geometry as the connector
62. These opposing fastening devices may then be removed after
providing temporary contact with the area 63 during the formation
process. The required acid electrolyte diffuses into area 63 along
the fibre material from the edge or from the bulk of the
electrode.
After the electrochemical conversion, the carbon fibre element at
step 17-5 with resultant lug can then undergo a further process
step to remove any porosity in area 63, to prevent or minimise or
reduce electrolyte entering the pores in the Pb network in 63 (as
subsequent discharge of the cell would then cause PbSO.sub.4 to
form, reducing or eliminating the conductive property of 63).
Removal or reduction of porosity may be achieved by for example:
compression and/or heating area 63, for example, by induction or
resistive heating, the region 63 is further dipped into a sealant
solution that leaves the pores filled with a polymer that does not
dissolve in the electrolyte, such a sealant solution includes for
example a resin, and filling some of the remaining pores in 63 by
electrode position of Pb from a strong solution of Pb ions.
To explain the electro deposition of Pb, an alternative embodiment
is illustrated in FIG. 18. One of the connectors 62 is replaced by
a mechanical fastening device comprising an internal lengthwise
conduit 67 and also supplied with sulphuric acid and also having
leady surfaces 66 arranged to physically contact the carbon fibre
element 1 on one side in the area 63 where paste material has
already been applied and a connection is desired. The device may be
fastened to an edge of the carbon fibre element or extend across
the carbon fibre element so long as the desired pasted area 63 is
captured by the leady surfaces 66 of the clamp. A suitable positive
electrode is installed in the (recirculating) electrolyte flow
entering and leaving 67 to complete a cell and current flow may
generate Pb within the inter-fibre space within area 63, as carried
out previously with a connector 62.
The leady surface 66 as shown in FIG. 18 may consist only of a
leady perimeter (ie otherwise open) or may be a porous leady
material, so that the electrolyte passing through the conduit 67
may permeate to the carbon fibre and paste.
After the above described formation process, a lead salt solution
(for example of PbNO3) may then be passed through the conduit 67 in
the connector 67 so that the lead pores that are in front of the
conduit are filled with lead. A metered amount of solution may be
injected into the conduit. The voltage applied between the positive
and negative electrodes is then adjusted to achieve a suitable
level so that lead is evenly deposited in the pores of the lug
zone. The injection of the lead salt solution and the
electrochemical deposition process is repeated until the pores are
close to being filled with lead. Successive injections will be
smaller and more difficult to achieve until no more injection or
deposition can be achieved. Collapse procedures or resin injection
may also be used at this point to remove any small accessible
porosity remaining. This also may be carried out as an alternative
to dipping step D above, but is more practical as a subsequent
step.
In an embodiment for forming a carbon fibre electrode of a Ni--Cd
battery or cell the lug may be formed of Cd and the paste comprise
Cd such as CdOH particles.
General
In a battery typically a lead-acid battery, the positive electrode
or electrodes, the negative electrode or electrodes, or both, may
be formed with a lug in accordance with the method(s) of the
invention. Preferably the current collector material and the fibres
thereof are flexible, which will assist in accommodating volume
changes of the active material attached to the current collector
material during battery cycling, and the microscale fibres may also
reinforce the active material, both assisting to reduce breaking
off ("shedding") of active material from the electrode in use.
In preferred embodiments the electrode fibres are inherently
conductive without requiring coating with a more conductive
material such as a metal to increase conductivity, and may be
carbon fibres which may in some embodiments be treated to increase
conductivity. In other embodiments the electrode fibres may be a
less conductive material, the fibres of which are coated with a
conductive or more conductive coating. In some embodiments the
fibres of the current collector material may be coated with Pb or a
Pb-based material. For example the negative electrode or electrodes
may be coated with Pb and the positive electrode(s) coated with Pb
and then thereon PbO.sub.2.
The current collector material may be a woven material, a knitted
material, or a non-woven material, such as a felt. The material may
comprise filaments extending in a major plane of the material with
each filament composed of multiple fibres, with optionally
connecting threads extending transversely across the filaments to
mechanically connect the filaments. The average depth of the
material may be at least 0.2 millimeters or at least 1 millimeter.
At least a majority of the fibres have a mean fibre diameter of
less than about 15 microns, more preferably less than or equal to
about 6 to about 7 microns.
The fibre surfaces of the material may be surface treated to
enhance attachment of the Pb-based particles by processing to
attach oxide particles or oxygen bearing chemical groups to the
fibres. Anodic oxidation of electric arc-treated carbon fibre
fabric also may convert it to a hydrophilic material. This may
assist an even distribution of the active particles through the
material and initial attraction of the Pb (covered with oxide
groups) to the carbon, by dipole-dipole attractions.
In some embodiments the conductive fibre material may be carbon
fibre material which has been thermally treated at an elevated
temperature, for example in the range 1000 to 4000.degree. C. In
some embodiments the conductive fibre material may be carbon fibre
material which has been treated by electric arc discharge. The
carbon fibre material may be electric arc treated by moving the
carbon fibre material within a reaction chamber either through an
electric arc in a gap between electrodes including multiple
adjacent electrodes on one side of the material, or past multiple
adjacent electrodes so that an electric arc exists between each of
the electrodes and the material.
In some embodiments the conductive fibre material may be felt or
other non-woven planar electrode material produced to very low
thickness such as for example 2.5 mm or less thickness by dividing
thicker material in plane. That is, the material may be cut in its
plane one or more times to divide a thicker non-woven material into
multiple sheets of similar length and width but reduces thickness
to the starting sheet.
In some embodiments the conductive fibre material may be woven
carbon fibre material may be woven from carbon fibre tows which
have been `stretch broken` ie a tow (bundle) of a larger number of
continuous carbon fibre filaments is stretched after manufacture to
break individual continuous filaments into shorter filaments and
separate lengthwise the ends of filaments at each break, which has
the effect of reducing the filament count of the carbon fibre tow.
The resulting reduced filament count tow is twisted (like a rope)
to maintain tow integrity. For example a tow of 50,000 continuous
filaments may be stretch broken to produce a much longer tow
composed of 600 shorter individual filaments which is then twisted,
for example. In some embodiments the conductive fibre material may
be carbon fibre material formed from carbon fibre tows which have
been `tow split` ie split from a higher filament count bundle of
carbon fibres (`tow`), into smaller tows. In some embodiments the
conductive fibre material may be carbon fibre material formed from
carbon fibre tows both split from a higher filament count bundle of
carbon fibres into smaller tows, and then stretch broken to break
individual continuous filaments into shorter filaments and separate
lengthwise the ends of filaments eat each break, further reducing
the filament count of the carbon fibre tows.
EXPERIMENTAL
Example 1--Lug Formation
In experimental work Pb lugs were formed on carbon fibre material
generally by the method described above with reference to FIG.
5.
To obtain Scanning Electron Microscope (SEM) images of the insides
of the lug region, the lugs were dipped in liquid Nitrogen and
cleaved post formation. FIGS. 6A and 6B are a set of SEM images
from a lug on a woven material with lead injected at a pressure of
10 bar. FIGS. 7A and 7B are another set of SEM images from a lug on
a felted material with lead injected again at a pressure of 10 bar.
Similarly FIGS. 8A and 8B are a set of SEM images from a lug on
woven material with lead injected at a pressure of 10 bar with an
epoxy applied to the top of the lug. FIGS. 6B, 7B, and 8B are at
higher magnification than FIGS. 6A, 7A, and 8A. In all of FIGS. 6A,
6B, 7A, 7B, 8A and 8B the pale grey material is the lead and the
long fibres are carbon fibres. The highest lead penetration of the
material was achieved with a carbon felt material, which is shown
in the series of SEM images of FIG. 7--lead clearly surrounding
each fibre with very minimal presence of voids. FIG. 7A shows full
width or cross section of the lug, and FIG. 7B shows a close up
(higher magnification) of the carbon fibres in the Pb (the holes
are where fibres have been pulled out during cleaving of the
lug).
In certain embodiments to reduce electrolyte penetration into voids
in the lug, potentially leading to lead conversion to lead sulphate
and so a loss of conductivity, epoxy was applied to the top of the
lug, to wick into the lug and prevent acid penetration. FIG. 8
shows the lug region with excellent epoxy penetration and minimal
voids.
Example 2--Lug Formation
The following two samples of lugs were attached to carbon felt by
edge impregnation of molten lead in the major plane of the felt
generally by the method described above with reference to FIG.
15.
The first sample was on carbon felt from Heilong Jiang in China
with solid volume fraction 7.2%, thickness 1.5 mm and mean diameter
of fibres 13.9 .mu.m and arc treated as described above. This lug
was made of two regions that lay next to each other--first a strip
of lead in a cavity along the edge of the felt and second a lead
matrix around the carbon fibres of the felt at its edge. By cutting
off the second area and carefully measuring its dimensions and
mass, together with determining the mass of a measured area of the
felt, one can calculate the voidage fraction within the matrix (see
below). This voidage was 22.5%. The resistivity of the matrix was
also determined by resistance measurement with a resistance meter
over a measured volume of the matrix. This resistivity was 0.32
mOhmmm, or 0.32/0.208=1.54, or 54% higher than that of pure lead at
room temperature.
FIG. 19 is an SEM image of this sample, showing holes where fibres
have been pulled out during brittle fracture using cryogenic
conditions, but otherwise shows lead surrounding most fibres. Two
parts show some localised lack of lead, where fibres were drawn
together.
FIG. 21 is an SEM image of a second lug sample produced in the same
way but on carbon felt from SGL in Germany with solid volume
fraction of 4.6%, 2.5 mm thick and mean fibre diameter of 9.1 .mu.m
also arc treated. This was infiltrated as with the first sample
yielding a higher voidage fraction of 41% and resistivity of 0.61
mOhmmm, or almost 3 times that of pure lead. The fracture surface
shows large areas of fibres that are not contacting lead.
The connection resistances of both samples were <50 mOhms.)
The methods of measurement used were as follows:
Resistivity:
Strips of the connector where carbon felt were surrounded by lead,
were cut off with a guillotine, and the ends were held by the
clamps of a resistance meter. The length/between the clamps and the
observed cross-sectional area A were used in the expression
Resistivity=(Resistance)(Area)/(length) to calculate the
resistivity.
Voidage:
The strips were weighed and the mass divided by the area to get an
overall mass areal density. The same was done for samples of the
carbon felt to obtain a carbon areal density, and this was
subtracted from the first to obtain the lead areal density.
Dividing this by the density of pure lead and by the thickness of
the felt yielded the volume fraction of lead in the composite
strips. Thus the voidage was obtained by subtracting both the lead
volume fraction and the carbon volume fraction from 1.0, the total
volume fraction.
Resistance:
Aluminium bars 8 mm square were used for contacts onto the carbon
felt, one each side of the felt, with a standard contact force
provided by the clamps of the resistance meter. Two pairs of such
contacts were spaced at difference distances (10 to 80 mm) and 5
resistances were recorded at different distances over this range.
The closely linear plot of resistance versus distance provided a
slope (which yielded the resistivity of the felt when multiplied by
the cross-sectional area) and an intercept, which was twice the
contact/felt resistance. Then one set of contacts were used on an
electrode with a connector on one end, with again different
placings of the contacts along the electrode, and the other meter
clamp attached to the lead tab at one end of the connector. A plot
of resistance versus distance again gave a linear plot, with
intercept equal to the sum of one contact/felt resistance plus the
electrode connector resistance we require. Thus the latter was
obtained by subtraction of the contact/felt resistance.
Example 3--Pb-Acid Cell CCA Performance with Electrode Comprising
Lug
Electrode & Cell Construction:
An electrode was constructed from arc-treated carbon fibre felt
having a specific weight of 238 g/m.sup.2, a thickness of 2.93 mm,
and a carbon volume fraction .about.5.8%. After arc-treatment the
felt had a specific weight of 204 g/m.sup.2, was 2.5 mm thick, and
had a carbon volume fraction .about.5.7%. The carbon felt section
was rectangular in shape and had previously had a Pb lug formed
along one edge by edge impregnation of molten lead in the major
plane of the felt generally by the method described above with
reference to FIG. 15, so that Pb material of the lug penetrated
fully through the lug zone of the carbon felt material from one
side to the other.
Paste was prepared with 19.5 g of leady oxide having .about.5.1% Pb
content, 3.36 g of diluted sulphuric acid, 2.24 g of Vanisperse A
as an expander and water solution to achieve 0.10 wt % of expander
in the prepared paste, and 0.16 g of Barium Sulphate. The paste was
mixed in a bath for 2 minutes with ultrasound at a frequency of 54
kHz.
The electrode was pasted with an even distribution of paste, also
under ultrasound vibration on for .about.1 min, via an ultra-sound
vibrating plate until a majority of the paste had penetrated into
the felt. The paste was applied to the electrode so that it
contacted the lug Pb along the length of the boundary between the
lug Pb and the non-lug Pb impregnated carbon felt (not only at the
surface on either side but also through the thickness of the carbon
felt material at this boundary). The total amount of mass loaded
into the carbon felt was 18.15 g where the achieved capacity (low
current discharging) was 2.52 Ah (i.e. 61% (68.2%) of the
theoretical capacity). The pasted electrode active area (excluding
the lug) had dimensions: length of 60.6 mm, width of 43.3 mm, and
thickness of 2.52 mm Therefore the achieved lead loading per volume
(pasted density of the electrode based on the mass loaded on to the
electrode) was about 2.62 g/cm.sup.3
The electrode was then built into a test cell, as a negative was
sandwiched between two (one on each side) traditional positive
plates of comparable size and subjected to formation charging.
Testing & Results:
The cell was subjected to SAE -18.degree. C. CCA (cold cranking
amps) tests. In particular an automotive battery should be able to
deliver high current for engine starting, at low temperature, and a
CCA test tests the ability of a battery to do so. Test currents
were 310 mA/cm2 opposed electrode area, respectively. Having
successfully passed the 310 mA/cm2 test, the electrode pasted right
up to the lug was further tested at successively higher currents,
eventually achieving a rating of 390 mA/cm2. FIG. 21 shows result
of the CCA performance test and shows that the electrode had very
good CCA performance.
The foregoing describes the invention including preferred forms
thereof and alterations and modifications as will be obvious to one
skilled in the art are intended to be incorporated in the scope
thereof as defined in the accompanying claims.
* * * * *